1. Field of the Invention
The invention relates in general to a polishing apparatus and a pad replacing method thereof, and more particularly to a polishing apparatus capable of automatically replacing a polishing pad and a pad replacing method thereof.
2. Description of the Related Art
As semiconductor technology develops, layout with higher density develops continuously. In the semiconductor manufacturing process, layout with higher density requires better surface flatness of the chip for increasing the accuracy of the lithography process. Therefore, chemical mechanical polishing (CMP) has become an important technology in the semiconductor manufacturing process.
FIG. 1 illustrates a conventional polishing apparatus. Please referring to FIG. 1, the polishing apparatus 900 is an inverted-type chemical mechanical polishing apparatus 900. The polishing apparatus 900 includes a polishing head 930, a carrier 960 and a slurry injector 970. A wafer 800 is placed on the carrier 960. The polishing head 930 is disposed over the wafer 800. A polishing pad 700 is adhered to a polishing surface 930a of the polishing head 930 by an adhesive. The material of the polishing pad 700 is polyurethane for example. In the polishing process, the polishing head 930 and the wafer 800 rotate along opposite directions. The polishing head 930 applies a proper force F to the wafer 800, and the slurry injector 970 injects slurry 971 between the wafer 800 and the polishing pad 700, for removing surface roughness of the wafer 800. As a result, the required flatness can be achieved.
In the semiconductor manufacturing apparatus, the yield rate (wafer number/working time) is an important factor in evaluating the apparatus. The polishing speed, wafer placing speed or pad replacing time can affect the yield rate of the apparatus.
After the polishing apparatus 900 operates for a while, the polishing pad 700 is worn out gradually. The polishing apparatus 900 needs a new polishing pad 700 for continuing the polishing process. The polishing pad 700 is adhered to the polishing head 930 by the adhesive. Therefore, when the polishing pad 700 is replaced, a tool, such as a rasp, is needed to completely remove the polishing pad 700. Then, a new polishing pad 700 is adhered. It takes a long time to replace the polishing pad. Therefore, the polishing apparatus 900 also stops working for a long time. As a result, the yield rate of the polishing apparatus 900 is decreased significantly, and the polishing head 930 might be damaged.
Furthermore, the hardness and holes of each polishing pad 700 are corresponding to the manufacturing conditions and the object (such as metal conductor or dielectric) needed to be removed from the surface of the wafer 800. When the manufacturing conditions or the object needed to be removed is different, different polishing pad 700 is used. However, when the polishing pad 700 is replaced, the old polishing pad 700 is damaged and can no longer be used, which is very wasteful. Therefore, the manufacturing conditions and the object needed to be removed can change randomly. As a result, the flexibility of the manufacturing process of the polishing apparatus 900 is lowered.
Therefore, it is very important to develop a polishing apparatus to solve the above problems.